NATURAL LANGUAGE PROCESSING Text Book: Artificial Intelligence by Luger, 4th edition, Pearson Education Reference Material: Artificial Intelligence by Elaine Rich and Kevin Knight, 2nd edition, TATA McGraw Hill Education. SOHAIL SHAHZAD ROLL NO: 15134 GCU FAISALABAD

What is Natural Language Refers to the language spoken and understand by people, e.g. English, Urdu, as opposed to artificial languages, like C++, Java etc.

What is Natural Language Processing Natural Language Processing NLP refers to AI method of communicating with an intelligent systems using everyday natural language such as English. NLP is related to human computer interaction. NLP encompasses anything a computer needs to understand natural language and also generate natural language. NLP is a subfield of artificial intelligence. The input and output of an NLP system can be- (i) Speech (II) Written Text

Components Of NLP There are two components of NLP Natural Language Understanding NLU Natural Language Generation NLG

Natural Language Understanding NLU There are two task. Mapping the given input in natural language into useful representation. Analyzing different aspects of the language

Natural Language Generation NLG It is the process of producing meaningful phrases and sentences in the form of natural language form some internal representation. It involves. Text Planning: It includes retrieving the relevant content from knowledge base. Sentence Planning: It includes choosing required words, forming meaningful phrases, setting tome of the sentence. Text Realization: It is mapping sentence plan into sentence structure.

Difficulties in NLU It is very ambiguous. There can be different levels of ambiguity. Lexical Ambiguity: It is at very primitive level such as word level. For example, treating the word “board” as noun or verb. Syntax Level Ambiguity: A sentence can be parsed in different ways. For example, “He lifted the beetle with red cap” or “Did he use cap to lift the beetle”.

Difficulties in NLU 3) Referential Ambiguity: Referring to something using pronouns. For example, Ali went to Hussain. He said, “I am tired.” Exactly who is tired.

Step’s in NLU There are general five steps Lexical Analysis: It involves identifying and analyzing the structure of words. Lexicon of a language means the collection of words and phrases in a language. Lexical analysis is dividing the whole chunk of txt into paragraphs, sentences and words.

Difficulties in NLU Syntactic Analysis: It involves analysis of words in the sentence for grammar and arranging words in a manner that shows the relationship among the words. The sentence such as The school goes to boy” is rejected by English syntactic analyzer. Semantic Analysis: It draws the exact meaning or the dictionary meaning from the text. The semantic analyzer disregards sentence such as “ hot ice-cream”.

Difficulties in NLU 4) Discourse Integration: The meaning of any sentence depends upon the meaning of the sentence just before it. In addition, it also brings about the meaning of immediately succeeding sentence. 5) Pragmatic Analysis: During this, what was said is re-interpreted on what it actually meant. It involves deriving those aspects of language which require real world knowledge.

Implementation Aspects Of Syntactic Analysis There are a number of algorithms researchers have developed for syntactic analysis, bit we consider only the following simple methods. Context Free Grammar Top Down Parser

Implementation Aspects Of Syntactic Analysis Context Free Grammar It is the grammar that consists rules with a single symbol on the left hand side of the rewrite rules. Let us create grammar to parse a sentence “The bird pecks the grains”. Articles DET − a | an | the Nouns − bird | birds | grain | grains Noun Phrase NP − Article + Noun | Article + Adjective + Noun= DET N | DET ADJ N Verbs − pecks | pecking | pecked Verb Phrase VP − NP V | V NP Adjectives ADJ − beautiful | small | chirping

Implementation Aspects Of Syntactic Analysis The parse tree breaks down the sentence into structured parts so that the computer can easily understand and process it. In order for the parsing algorithm to construct this parse tree, a set of rewrite rules, which describe what tree structures are legal, need to be constructed. These rules say that a certain symbol may be expanded in the tree by a sequence of other symbols. According to first order logic rule, ff there are two strings Noun Phrase NP and Verb Phrase VP, then the string combined by NP followed by VP is a sentence. The rewrite rules for the sentence are as follows

Implementation Aspects Of Syntactic Analysis S → NP VP NP → DET N | DET ADJ N VP → V NP Lexocon − DET → a | the ADJ → beautiful | perching N → bird | birds | grain | grains V → peck | pecks | pecking The parse tree can be created as shown

Implementation Aspects Of Syntactic Analysis

Implementation Aspects Of Syntactic Analysis Now consider the above rewrite rules. Since V can be replaced by both, "peck" or "pecks", sentences such as "The bird peck the grains" with wrong subject-verb agreement are also permitted.

Top Down Parser Here, the parser starts with the S symbol and attempts to rewrite it into a sequence of terminal symbols that matches the classes of the words in the input sentence until it consists entirely of terminal symbols. These are then checked with the input sentence to see if it matched. If not, the process is started over again with a different set of rules. This is repeated until a specific rule is found which describes the structure of the sentence.